In manufacturing of large-scale and high performance semiconductor devices including Large Scale Integrations (LSI) on a surface of a substrate, e.g., a semiconductor wafer (hereinafter, referred to as a “wafer”), it is necessary to form an ultra-fine pattern on the surface of the wafer. The pattern is formed by conducting a patterning process for the wafer coated with resist, which includes various processes such as an exposure process, a developing process, and a cleaning process. The wafer is then etched to transfer the resist pattern to the wafer, thereby forming the pattern on the surface of the wafer. After the etching process of the wafer, a cleaning process is performed in order to remove dusts or natural oxide films on the wafer.
In the cleaning process, for example, as schematically illustrated in FIG. 12A, a wafer W formed with a pattern 11 on a surface thereof is immersed in a processing liquid 101, such as a chemical liquid or a rinse liquid, or processing liquid 101 is supplied to the surface of wafer W. However, as the semiconductor devices are highly integrated, there occurs a problem of a pattern collapsing in which pattern 11 or the resist on the surface of the wafer collapses during a drying process of the processing liquid, after performing the cleaning process.
The pattern collapse refers to a phenomenon in which pattern 11 collapses toward the direction where larger quantity of processing liquid is remained when the processing liquid on left and right sides of pattern 11 is not uniformly dried after the cleaning process is completed, because the balance of the capillary force, which tensions pattern 11 in the left and right directions, is lost. FIG. 12B illustrates a state in which the processing liquid is dried on the outside regions of the left and right sides in which pattern 11 is not formed, while the processing liquid remains in the gap of pattern 11. As a result, pattern 11 on both the left and right sides collapses inwardly by the capillary force applied from the processing liquid left between patterns 11. The to pattern collapse is also a problem in the field of the MEMS (Micro-Electro-Mechanical System), which is manufactured by application of semiconductor manufacturing technology.
The capillary force that causes the pattern collapse is caused by the surface tension of the processing liquid applied in liquid/air interface between, for example, the atmosphere surrounding wafer W and the processing liquid left between patterns 11, after the cleaning process. Therefore, a processing method of drying the processing liquid (hereinafter, referred to as “a supercritical processing”) by using fluid in a supercritical state (supercritical fluid) in which interface is not formed between gas and liquid has been attracting attention.
In the supercritical processing method, as illustrated in FIG. 13A, for example, liquid on a surface of wafer W is substituted with supercritical fluid 102 within a sealed chamber and then supercritical fluid 102 is gradually discharged from the chamber. As a result, the surface of wafer W is substituted in a sequence of processing liquid→supercritical fluid→air atmosphere, so that it is possible to remove the processing liquid on the surface of wafer W without forming the liquid/air interface, thereby preventing the generation of pattern collapse.
For the fluid used in the supercritical processing, carbon oxide, hydrofluoro ether (HFE), hydrofluoro carbon (HFC), etc. are used. However, carbon oxide in the supercritical state has low miscibility with the processing liquid, so that there may be a case in which the carbon oxide in the supercritical state makes it difficult to substitute the processing liquid with the supercritical fluid. In the meantime, a fluorine compound, such as HFE or HFC, is satisfactorily miscible with the processing liquid, but a part of the fluorine compounds is pyrolyzed at a high temperature and a high pressure in which the processing liquid becomes the supercritical state, so that there is a case in which, for example, the fluorine compound discharges fluorine atoms in a state of HF.
For example, as illustrated in FIG. 13A, in the event that an SiO2 film 12 to is formed on the surface of wafer W, when the fluorine atoms are emitted from the fluorine compound, there is a concern that SiO2 film 12 is etched as illustrated in FIG. 13B. Further, the discharge of the fluorine atoms from the fluorine compound results in the deterioration of the property of the semiconductor device because the fluorine atoms may be injected into the semiconductor device of wafer W or pattern 11. Especially, when oxygen or moisture exists in the atmosphere in which the supercritical processing is performed, the oxygen or moisture becomes an ingredient facilitating the pyrolysis of the fluorine compound, so that SiO2 film 12 may be easily etched or the fluorine atoms may be easily injected into the device.
Japanese Laid-Open Patent Publication No. 2006-303316 (e.g., paragraphs 0035 through 0038) discloses a technology in which a mixture liquid of HFE, such as HCF2CF2OCH2CF3, CF3CHFCF2OCH2CF3, and CF3CHFCF2OCH2CF2CF3, is made in the supercritical state, the supercritical fluid is applied to a substrate processed with the cleaning process, and the substrate is dried. However, the disclosed technology does not take into account the problem of the discharge of the fluorine atoms from HFE.